This invention relates to improved cosmetic emulsions, especially to emulsions useful for moisturizing and conditioning the skin. This invention more particularly relates to cosmetic compositions using cationic emulsifiers, especially to cosmetically acceptable skin lotions or creams having an emulsified petrolatum or mineral oil base. In distinct embodiments, this invention also relates to methods for preparing skin care compositions emulsified by cationic surfactants and having a petrolatum or mineral oil base.
A normal horny layer of epidermis usually contains 10-20% of moisture which helps to impart elasticity, flexibility, or softness to the skin and to maintain a protective effect for the skin. When the moisture content decreases to less than 10% due to changes in environmental conditions or the like, the skin loses its elasticity and protective function and develops a so-called dry-skin condition which causes various skin problems.
A wide variety of emulsions have been used to moisturize skin. Both oil-in-water (water-out) emulsions and water-in-oil (oil-out) emulsions have been tried. Emulsifiers employed in these formulations have included anionic, nonionic, cationic, and mixtures thereof, although the more common commercial products have used anionic and nonionic emulsifiers.
One skin cream based on cationic emulsifiers that has been popular with consumers is CUREL lotion sold by Bausch & Lomb Incorporated. The product is a skin care composition which uses a quaternary ammonium compound as the sole emulsifying agent in an oil-in-water emulsion. By using particular quaternary ammonium compounds, superior properties for a hand care product result. Cosmetically acceptable products can be prepared, including a substantial quantity of petrolatum or mineral oil, in combination with fatty alcohols and fatty ester emollients. The composition has excellent tactile properties and, at the same time, provides good protection to the hands of the user. See U.S. Pat. No. 4,389,418.
Other skin care products using cationic surfactants are described in U.S. Pat. Nos. 4,781,918, 5,013,763, and 5,135,748.
Hydroxy (alpha and beta), keto, carboxylic, and dicarboxylic acids have long been used in a wide variety of retail cosmetic products to remove dead cells from the surface of the skin and to assist moisturization, thus providing a clearer and more beautiful complexion. See U.S. Pat. Nos. 3,879,537, 3,920,835, 3,984,566, 4,105,783, 4,197,316, 4,234,599, 4,380,549, and 5,691,171. Also see Smith, W. P., "Hydroxy Acids and Skin Aging," Cosmetics & Toiletries, Vol. 109, pp. 41-48 (September, 1994). They are components of interest in current cosmetic products because of the demand for products that diminish the appearance of fine lines on the face and improve the appearance of flaking or dry skin.
Treatments for dry skin often involve the application of hydrocarbons such as petrolatum or mineral oil to cover the skin with a hydrophobic occlusive film which prevents water loss from the skin surface to the environment. Other components such as the hydroxy acids mentioned above and hydrophilic humectants such as polyols, especially glycerin, are included in formulations to add moisture to the skin. It would be desirable to provide more effective formulations which not only prevent water loss from the skin but also act more effectively to directly hydrate dry skin.